1. The valuable contribution of observational studies to nephrology
K.J. Jager, V.S. Stel, C. Wanner, C. Zoccali, F.W. Dekker 
Kidney International 
Volume 72, Issue 6, Pages (September 2007)
DOI: /sj.ki
Copyright © 2007 International Society of Nephrology Terms and Conditions

2. Figure 1
Contribution of different study designs to clinical research. The increase in evidence from the bottom to the top only applies to studies on the effect of therapy (or other interventions). Footnote: As cross-sectional studies play a very limited role in studies on effects of therapy, this study design was not included in the figure.
Kidney International  , DOI: ( /sj.ki )
Copyright © 2007 International Society of Nephrology Terms and Conditions